Next year, more than a decade after coming to power, Labour will finally roll out across the country a large-scale programme aimed at driving more than 2.5m people claiming incapacity benefit back into the workforce.

The story of how such an important policy has taken so long to implement is a strange – and above all a long – one. Tony Blair and Gordon Brown, the joint architects of New Labour, “were convinced from very early on” that of all the problems of worklessness the government was facing, “this was the big one”, says an insider who was involved in welfare policy from the very beginning. So why did they take so long to do anything substantial about it?